In a known circuit arrangement for controlling a gear shift indicator of a motor vehicle drive, threshold limit values, ascertained for each gear by the vehicle manufacturer, for shifting into the next-higher gear are fed into an electronic read-only memory. During vehicle operation, the speed values and gas pedal positions that are ascertained on a continuous basis are compared with the threshold or limit values in a computer, and if the limit values are exceeded, a signal for shifting to a higher gear is triggered (German Patent Disclosure Document, laid open No. DE OS 31 28 080 Feb. 3, 1983). This arrangement has the disadvantage that the threshold or limit values must be ascertained for each vehicle type in accordance with the gear ratios of the gear steps and in accordance with the engine's power rating, based on an assumption that the engine is optimally tuned. Since after breaking in, engines may already have considerable fluctuations in power as compared with the rated value, and since in the course of time further power fluctuations are brought about by adjustments of the ignition or the carburetor or fuel injection pump, the threshold values ascertained by the manufacturer for gear shifting may be only approximate values. Furthermore, this method does not take into consideration changing load conditions or the grade of the roadway while driving when indicating a shift into a higher gear.
With the present invention, the object is to develop a method for determining the threshold values for shifting gears which enables optimum power at minimum fuel consumption, regardless of the size of the engine, the vehicle load or the gear ratios.